Silicon carbide is well known for its high strength, hardness, and its resistance to oxidation, corrosion, and abrasion. Consequently, silicon carbide and reaction-bonded silicon carbide are employed in many applications requiring these properties. Reaction-bonded silicon carbide includes a discontinuous silicon carbide grain phase held together within a continuous bond phase matrix.
For example, blocks based on silicon carbide (SiC), bound by a matrix of silicon nitride (Si3N4) are known. The materials for such blocks are described, for example, in U.S. Pat. No. 2,752,258. They improve the compromise between oxidation resistance, mechanical strength (erosion), and thermal conductivity relative to carbon blocks. Such blocks are obtained by reaction sintering of a mixture of silicon carbide and silicon, with nitrogen deriving from firing in a nitrogen atmosphere.
A heterogeneous nitridation reaction also can be employed to yield bond phases other than silicon nitride. For example, reaction-bonded silicon carbide, in which the major component of the bond phase is silicon oxynitride, (Si2ON2), can be produced by nitriding a mixture including particulate silicon carbide, silicon metal powder, and an oxygen source.
However, typically silicon oxynitride bonded silicon carbide will exhibit increases in volume change upon extended exposure to oxidative stress, and so can be unsuitable for certain applications, such as use as tiles in some types of incinerators.
A need therefore exists for a silicon oxynitride bonded silicon carbide refractory material that significantly reduces or eliminates the above-referenced problems.